This invention relates to engine lubrication systems and, more particularly, to variable displacement pumps for supplying engine oil to internal combustion engines.
It is known in the art relating to engine oil pumps to use positive displacement pumps to supply pressurized oil to lubrication and hydraulic systems of the engine. These pumps are typically fixed displacement pumps that rely on a pressure responsive valve to regulate maximum oil pressure, thus regulating engine oil flow. Automotive engines have used both external pinion gears, commonly referred to as spur gear pumps, and internal/external pinion gears, commonly referred to as gerotor, crescent, etc., gear pumps, to serve as the pumping elements. Because these are fixed displacement pumps, their output flow is directly proportional to their operational speed. Similarly, the torque required to drive these pumps is proportional to both the pressure rise across the pump and their theoretical displacement. As used in automotive engines that directly drive the pumps, the drive torque of these pumps increases directly with the engine operating speed.
Use of fixed displacement pumps to supply a minimum oil pressure under hot idle conditions requires using a pump that is larger in displacement than is needed for providing adequate oil flow and pressure at other engine speeds where oil flow is increased and oil pressures are higher.
Thus, at speeds other than idle, use of a fixed displacement pump creates a significant parasitic energy loss for the engine.
The present invention provides a variable displacement vane engine oil pump which is small in size, has excellent volumetric efficiency at low speeds and significantly reduces parasitic losses at speeds greater than idle.
In a specific embodiment, a variable displacement vane pump includes a housing inside of which a slide ring is retained within the housing wall by a slide ring pivot. A rotor with slide vanes and a hex shaft drive of the rotor are located within the slide ring. Inlet and outlet ports allow fluid to enter and exit the pumping volume within the slide ring. A pick-up tube extends from the bottom of the pump and connects with the inlet port. A modular pressure relief valve assembly screws into a pump outlet passage.
A flange extends from the slide ring on a side opposite the slide ring pivot. The flange acts as a slide stop, a slide seal support, and a slide spring tab. A slide seal is attached to the slide seal support and extends beyond the slide seal support to sealingly engage the housing wall. A pressure control chamber is formed in a space between the housing wall, the slide ring, the slide stop and the slide seal. A reaction spring is located between the housing wall and the slide spring tab and is opposite the pressure control chamber. The spring urges the slide ring toward a maximum displacement position of the rotor wall.
A variable displacement vane pump in accordance with the invention may be driven by a camshaft through a cross-axis gear that turns the pump at a slower rate than the engine crankshaft speed. A ported pressure signal from a rear main bearing cap, to which the pump is mounted by a single bolt, acts on the pump""s slide ring to cause it to pivot against the spring, thereby decreasing the pump""s displacement. Use of the ported pressure signal provides a closed loop pressure control from the backside of the crankshaft rear main bearing, which prevents pressure sag in the engine lubrication system due to high component flow restriction or oil aeration.
The slide is sealed on its end opposite the pivot and outside the slide stop, which biases the pressure required to initiate the slide ring movement. Once the slide ring moves off its stop, the pressure signal acts on a larger area of the slide ring to further move it until the force becomes balanced with a reaction spring. As a result, the pump is capable of producing a relatively flat oil pressure regulation curve. A modular pressure relief ball valve assembly attached to the pump outlet further limits pressure transients under cold engine conditions.
Inlet and outlet ports of the pump are preferably on opposite sides of the vanes, which prevents the entrapment of gases in the pump chambers. The combination of the slide stop, the slide seal support and the slide spring tab into one component also aids in keeping the size of the pump small.
These and other features and advantages of the invention will be more fully understood from the following description of certain specific embodiments of the invention taken together with the accompanying drawings.